The herbicidal activity of a great number of derivatives of variously substituted pyridyloxyphenoxypropionic acids is well known in the art, see for example, European Patent No. 483. The variations in herbicidal effectiveness of the optically active isomers of these compounds is also known, the R isomer being the most active herbicide, and this is taught, for example, in European Patent Application Nos. 2800, 3890 and 6608, German OLS No. 29 49 728 and British Pat. No. 2,042,503.